Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$206.61	6.371%	$219.7731	$219.77	$219.75	$219.80
Purchase #2	$230.60	5.752%	$243.8641	$243.86	$243.85	$243.90
Purchase #3	$243.60	10.241%	$268.5471	$268.55	$268.55	$268.50
Purchase #4	$190.47	5.382%	$200.7211	$200.72	$200.70	$200.70
Purchase #5	$202.54	4.592%	$211.8406	$211.84	$211.85	$211.80
Purchase #6	$35.27	7.782%	$38.0147	$38.01	$38.00	$38.00
Purchase #7	$76.63	6.819%	$81.8554	$81.86	$81.85	$81.90
7 purchase totals =	$1,185.72		$1,264.6161	$1,264.61	$1,264.55	$1,264.60